Variable electronic capacitance device



March 8, 1949. Y LABIN ET AL 2,463,632

VARIABLE ELECTRONIC CAPACITANCE DEVICE Filed Aug. 11, 1944 VI Amy! 2 Sheets-Sheet 1 16%; 16d 1% W 5 w II lllll I AND SLZ'VMLD] Z1 Z2 Z0 Z mmvrozes ATTORNEY March 8, 1949. E. LABIN ET AL VARIABLE ELECTRONIC CAPACITANCE DEVICE 2 Sheets-Sheet 2 Filed Aug. 11, 1944 II/IIIII Z0 Z0]! MARC ZTEGLER EDOUARD LABIN ANDRESZEVZALDZ INVENTORS BY I ATZURZVEY.

Patented Mar. 8, 1949 2,463,632 VARIABLE ELECTRONIC CAPACITANCE DEVI Edouard Labin and An dres Levialdi, Buenos Aires,

Argentina, and Marc Ziegler, Toronto, Ontario,

Canada, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application August 11, 1944, Serial No. 549,080 3 Claims. (Cl. 315-58) This invention relates to an electronic reactance device and more particularly to an electronic capacitance device designed to provide between a pair of utility terminals a pure capacitance variable in accordance with an electrical control potential.

Electronic reactance is widely used in the radio art and a wide variety of circuits providing electronic reactance are already known. However, in most of the known circuits the electronic reactance is obtained by feeding back to the control electrode, in a definite phase relationship, part of the voltage present at the anode of a thermionic discharge tube. The main disadvantages of the known feedback reactance circuits consist in that a heavy resistive load is present between the utility terminals of the circuit and that the created electronic reactance is rather low. The utilization of the known circuits of the above type is further limited by the danger of oscillations occurring in the circuit. In fact, the electronic reactance is generated at the output terminals of a rather complicated circuit providing a complete impedance instead of a pure reactance and including a plurality of circuit elements all susceptible to variations and thus influencing the ultimate value and stability of the electronic reactance obtained.

In contradistinction to the known electronic reactance circuits, the variable electronic capacitance device, according to our invention, does not use any form of feedback and provides a perfectly pure reactance of a value which does not depend on circuit parameters but only on the current density of the generated electron beam and the magnitude of the accelerating potential used. It is therefore one of the main objects of the present invention to provide an electronic device having a pair of utility terminals which, if connected to an external tension, represent for this tension a capacitance which can be easily controlled by varying the intensity of the electron beam.

A further object of the present invention is to provide an electronic device having a pair of utility terminals between which a capacitance will be obtained whose value will be considerably larger than that due to the physical dimensions and distance between the electrodes to which these utility terminals are connected, and which also will be considerably larger than that obtainable with the known electronic reactance circuits or devices.

These and other objects and advantages of the present invention will become apparent from the detailed description thereof taken in connection with the accompanying drawings forming part of the specification and wherein:

Fig. 1 illustrates one preferred embodiment of the variable electronic capacitance device according to the present invention utilizing a laminar electron beam.

Fig. 2 is an explanatory diagram referring to the operation of the capacitance device according to the present invention.

Fig. 3 illustrates a modification difiering from that of Fig. 1 in that a plurality of parallel laminar electron beams are used to obtain a large capacitance in a reduced space.

Fig. 4 exemplifies another embodiment of the electronic capacitance device according to the present invention.

Fig. 5 is a cross section indicated in Fig. 4.

Fig. 6 illustrates a further embodiment of the electronic capacitance device according to the present invention difiering from those of the previous figures in that an electron beam of circular cross section is used, and

Fig. '7 is a cross section indicated in Fig. 6.

The same reference characters indicate like or corresponding parts or elements throughout the drawings.

Referring now to Fig. 1 it can be seen that the the electronic capacitance device according to the present invention comprises a. hermetically sealed and evacuated envelope l0 including an eelctrode system H for generating a laminar beam of electrons H, the main section of which must be conceived in a plane perpendicular to the plane of the drawing. This electrode system is connected by means of terminals I3 and [4 to a supply source not shown in the drawings and is usually consituated by a filament, a cathode and sometimes a Wehnelt electrode and is adapted to generate a laminar beam l2. A control grid l5 and an accelerating anode [6 provided with an elongated slot I6 are located in the path of electron beam l2 and constitute together with a second anode I! and a target or collector electrode IS, an electron lens system designed to concentrate and to direct the generated electron beam l2 toward an elongated slot l 1' provided in the second accelerating anode l7. Through slot ll, electron beam l2 enters into a substantially rectangular chamber i9 formed of metal walls I9 electrically connected to and supported by second accelerating anode l1 and target electrode l 8, so that the electron beam traverses said chamber taken on the lines 55 taken on the lines 1-! l9 before impinging upon collector electrode it. As can be seen in the drawing, the first accelerating anode I6 is connected to a point of intermediate positive potential of a direct current supply 20 the negative pole 2!! of which is connected to terminal l3 of electrode system H to ground, while its positive pole 2G" is connected directly to second anode ll and collector it, so that chamber IQ encloses a practically perfect equipotential space which cannot influence either the path or the focussing of the electron beam i2 on its passage from slot ll to target 58.

Control grid or electrode i5 is connected through a grid leak resistor 2! to the negative pole of a bias supply source '22, and to one terminal 23 of a control circuit, the other terminal 24 of which is connected to ground, so that the intensity of the generated electron beam l2 can be adjusted in accordance with the amplitude of a control potential E applied between control terminal 23 and ground,

Equipotential chamber it encloses a capacitor 25 formed of electrodes 26 and 2t of any con venient shape but covering, in a direction perpendicular to the plane of the drawing, the entire width of the laminar electron beam i2. In Figs. 1 and 2 electrodes 26 and 26' have been curved to avoid the absorption of electrons from the passing electron beam deviated from its straight path due to the potential applied to these electrodes. It will be understood however, that plane metal plates may be also used for the same purpose. Electrodes 25 and 26 are connected to utility terminals 21 and 28, respectively, and are located equidistantly from the straight path of electron beam 12. Utility terminals 21 and 28 are those between which appears the desired electronic capacitance as will be explained hereinafter. They can be connected, for instance, to a load impedance Z formed of a tuned circuit in cluding a coil 29 and tuning capacitor 39, so that the electronic capacitance forming part of a circuit and, as will be shown, depending upon the accelerating potential applied to target electrode I8 and the current intensity of electron beam IE, will allow of any convenient control of said circuit by varying the control potential or by changing the accelerating potential applied to target electrode I8.

Fig. 2 is an enlarged and perspective view of a pair of electrodes 26 and 26 arranged similarly as electrodes 26 and 26 but shown, for the sake of simplicity, as plane and rectangular plates located parallel to and equidistantly from the capacitance obtained, can be easily appreciated straight path of the electrons, indicated with the broken line l2, of a substantially laminar electron beam I2" carrying a current intensity of J amperes with the velocity of V m/s. Electrodes 26" and 26 are each d m. long and w m. wide, and are separated from each other by s m., each electrode being further connected to utility terminals 2? and 28, respectively. The width of electron beam 12' is substantially equal to the width w of electrodes 25 and 25".

It will be understood that electrodes 25" and 26 constitute a capacitor the cold capacitance of which, i. e. the capacitance in absence of electron beam I2", is defined by the formula if the dimensions are in meters. Assuming now that utility terminals 2'! and 2B are connected to a potential mt), electron beam H2", in passing between these electrodes, will be deviated from the straight line l2 in accordance with the variations of the function u(t), as indicated schematically by the sinusoidal line 3|. Now, assuming that the passage time of the electrons is very small against the period of variations of function Mt), it can be shown that the displacement of electron beam 12 will induce in electrodes 26" and 28" a current 1(23) which will be given by the formula du Z: 2 541.7121? wherein can be called the geometric factor of the capacitance the time of passage of the electrons between electrodes 26 and 26".

It will be understood by those skilled in the art that the factor .6.9.7 constitutes an elec tronic capacitance Ce which is added to the cold" capacitance Co, depending merely upon the physi cal dimensions of the capacitor formed of electrodes 2t" and 26", so that the ultimate utility capacitance present between terminals 2i" and 28', and hence between utility terminals 2! and 28 of the electronic capacitance device according to Fig. 1, will correspond to the sum of the cold. and the electronic capacitances Co and Ce. Theory shows that as long as 7' is kept small with respect to period of mi), no positive term will appear in the relation between 2' and u, so that in fact a perfectly pure reactance will be obtained.

As can be seen from the above formula defining the electronic capacitance present between electrodes 26 and 28', its value is directly proportional to the current intensity J of the electron beam passing between the electrodes, so that a potential E applied to control grid IE will vary the value of the electronic capacitance appearing between utility terminals 21 and 28, and hence will also vary for instance the resonant frequency of the tuned circuit Z.

The order of magnitude of the variable utility by assuming that electrodes 26 and 26' of the electronic capacitance device shown in Fig. 1 are 2 cm. wide and 2 cm. long and that a separation of 0,5 cm. is used. Then, the cold capacitance Co present between utility terminals 21 and 28 is approximately 0,? ,u F. Now, assuming an electron beam carrying a current of 5,4 mA and an accelerating potential of U=9 volt, the electronic capacitance present between utility terminals 21 and 28 will be approximately 8 al so that the ultimate utility capacitance will be variable between 0,? and 8,7 B. The value of 8 ,lL/LF and, still more, the range between 0,? and 3,7, are quite considerable. Furthermore, since the electronic capacitance device, according to the present invention, represents a substantially pure capacitance without'any resistance, it can be connected directly across any tuned circuit without changing the operating conditions thereof.v

A limiting condition of the electronic capacitance according to the present invention is that the time of passage of the electrons between electrodes 26 and 26' should be considerably smaller than the period of the alternating tension generated or present across utility terminals 21 and 28.

Another limitation of the device, according to the present invention, consists in that the potential appearing across utility terminals 21 and 28 should be substantially smaller than twice the accelerating potential U divided by the geometric factor 6, in order to avoid the striking of the electron beam against electrodes 26 and 26'. For the example given, this would mean that the tension at terminals 21 and 28 should not be higher than 1 volt. However, it should be borne in mind that a similar limitation exists for the known reactance tube circuits in which the potential which can be applied to the terminals between which the utility reactance is obtained, is also limited by the possibility of autooscillations.

In the electronic capacitance device, according to the present invention, the ultimate capacitance obtainable between utility terminals 2'! and 28 is limited by the current intensity of the electron beam and the physical dimensions of electrodes 26 and 26'. Hence, one means for obtaining a larger electronic capacitance consists in utilizing an electron beam with higher current intensity as shown in the drawing of Fig. 3 in which an electronic capacitance device is schematically shown utilizing a plurality of parallel and superimposed laminar beams 12a, generated by an electrode system not shown in the drawing. This parallel beam capacitance device also includes a control grid (not visible) and a first accelerating electrode lBa, partly visible through the opening of the envelope Illa and provided with a plurality of elongated slots I6'a. In a similar way, the second accelerating anode Ila of the rectangular equipotential chamber ISa is provided with an equal number of elongated slots ll'a, through which electron beams |2a penetrate into equipotential chamber l9a before striking against collector or target electrode [8a.

Equipotential chamber l9a includes a capacitor 25a formed of electrodes each having a plurality of vanes interleaving with the vanes of the other electrode. As can be seen in the drawing, vanes 26a forming one electrode and electrically interconnected by means of a conducting member 32, are coupled to utility terminal 21a, while vanes 26'a, corresponding to the other electrode and electrically interconnected by means of a conducting member 33, are coupled to utility terminal 28a of the parallel beam electronic capacitance device. The ultimate utility capacitance obtainable between utility terminals 21a and 28a will be that of the precedent case multiplied by the number of electron beams IZa. The advantage of the electronic capacitance device, according to Fig. 3 with respect to that shown in Fig. 1, consists in that a larger utility capacitance is obtained without lowering the permissible higher limit of the utility frequency, since the transit time of the electrons between the electrodes remains substantially the same as in the device according to Fig. 1, as long as the geometrical factor of the electrodes is not modified. Furthermore, a larger electronic capacitance is obtained without lowering the accelerating voltage U with the subseuent limitations of the amplitude of the working voltage U, which can be tolerated at the utility terminals of the electronic capacitance device, according to the invention.

The schematic drawings of Figs. 4 and 5 illustrate another preferred embodiment of the electronic capacitance device according to the present invention, in which a large utility capacitance is obtained using one electron beam only, since sometimes it may be desirable to obtain a large capacitance, without resorting to a cathode system for generating a plurality of electron beams. The electronic capacitance, according to Fig. 4, comprises a substantially rectangular envelope IOb, including a cathode system I I, a control electrode l5 and a first accelerating anode Hi arranged in a manner similiar to that disclosed in Fig. 1. A second accelerating anode Nb and a collector or target electrode lBb form part of an equipotential chamber l9'b into which the laminar electron beam l2b penetrates through an elongated slot I 'l'b provided in accelerating anode l'lb forming the front wall of this equipotential chamber.

Equipotential chamber l9'b includes a capacitor 25b similar to that disclosed in the drawing of Fig. 3, and further contains field coils 34 and 35 connected in parallel to terminals 36 and 31, to which a source of magnetizing current (not shown in the drawings) is applied.

Each field coil 34 or 35 is formed of two rectangular coils of small rectangular cross section, arranged parallel and close to the lateral walls of equipotential chamber l9'b, in the vicinity of target electrode l8b or second accelerating anode l'lb, respectively, as can be observed in the drawing of Fig. 5. Coils 34 are centered on electrode 2Bb of capacitor 25b, and thus will generate an electromagnetic field substantially perpendicular to the plane of the drawing, so that electron beam I212, after having traversed the interelectrode space between electrodes 26b and 26b, is deviated due to the field generated by coils 34 and is directed toward the adjacent and lower interelectrode space between electrodes 26'b and 26b. The electron beam, after having traversed the space between electrodes 26'!) and 26b in an opposite direction, penetrates into the magnetic field generated by coils 35 and hence is turned back toward the space between the lowest electrodes 26b and 2Bb, now travelling in the original direction toward collector or target electrode I817. Thus, electron beam l2a passes between all electrodes of capacitor 25b connected to utility terminals 21b and 28b and induces in these electrodes a current according to the variations in the utility potential present at these terminals, the ultimate utility capacitance obtainable being equal to that of the electronic capacitance device according to Fig. 3. However, it should be borne in mind that the time of transit of the electrons between elongated entrance slot "'22 and collector electrode [8b not only has been increased to n-l times the transit time present in the devices illustrated in Figs. 1 and 3 (n being the total number of the capacitor electrodes), but also includes the substantially semicircular paths described by the electrons due to the director magnetic fields generated by coils 34 and 35.

The electronic capacitance devices illustrated in Figs. 1 to 5 have in common the utilization of substantially laminar electron beams and substantially plane and parallel electrodes enclosed in a rectangular equipotential chamber. Figs. 6 and 7 illustrate electronic capacitance devices according to the present invention in which an electron beam of annular cross section and a capacitor formed of concentric circular electrodes are used, so that a relatively large utility capacitance can be obtained in a reduced space.

As can be seen in the drawing, the electronic capacitance device illustrated in Figs. 6 and comprises a tubular envelope 3B of conventionai design, including at one end a cathode system 39 designed for generating an electron beam dd of annular cross section. Similar to the electronic capacitance devices shown in the previous figures, a control grid ll and accelerating anodes l2 and 43, provided with annular slots es and t3, respectively, are arranged in front of cathode is stem Sill to control the intensity and to direct electron beam lil toward the circular slot 43 pro vided in second accelerating anode as which, together with circular target electrode M and walls 15, forms a circular equipotential chamber connected to the positive pole M" of the low tension DA). supply 29.

Equipotential chamber M3 includes a capacitor c formed of two cylindrical and concentric electrodes 26c and 26'0 connected to utility terminals Z'i'c and 280, respectively. Electrodes 25c and Elic are concentrically arranged with respect to the circular entrance slot at, so that the nular electron beam Ml, after entering e uipotential chamber 45', travels within the interelectrode space limited by these electrodes. It will be understood by those skilled in the art that, due to the tension present at utility terminals 2'50 and 280, electron beam 46 will deviate from its mean path in a radial expansion or contraction placement, inducing in electrodes 25c and 25'0 a current i=A- L (Ft if the transit time oi the electrons is short with respect to the period of the tension mt). Hence, as before, an electronic capacitance A will be created between utility terminals tie and 230, this factor A being determined, already explained hereinbefore, by the accelerating potential U, the current carrying capacity J of the an nular beam 69, and the physical dimensions of capacitor 250. It will be also understood that, in order to increase the obtainable electronic capacitance, a plurality of concentrically arranged cylindrical electrodes can be used in combination with the corresponding number of annular electron beams.

In general, it is an essential feature of electronic capacitance devices, according to our invention, that the electron beams used are high intensity beams formed of very low velocity electrons. den-cc, these electron beams can be characterized as high conductance beams having conductivity of the order of millimhos, while in the usual electronic devices or tubes, for instance, cathode-ray tubes, beams having a conductivity of a few hundredths of a micromhos are used.

While we have shown our electronic capacitancc devices as utilizing electron beam intensity control means to obtain a variation of the utility capacitance, it will be understood that a variation of the accelerating potential applied to the target electrode can also be used for the same purpose. Furthermore, the capacitor electrodes enclosed in the equipotential chamber can be shaped to suit the particular performance characteristics of the device. Hence, it will be apparent to one skilled in the art that many modifications may be made without departing from the scope of our invention, as set forth in the appended claims.

We claim:

1. A variable electronic capacitance device comprising an evacuated envelope including means for generating a plurality of electron beams, a low-potential electron accelerating and collectin means constituted by an equipotential chamber having a plurality of slots looking toward said electron beam generating means and including a capacitor having tWo electrodes con nected to a pair of utility terminals and each constituted by a plurality of vanes, the vanes of one electrode interleaving with the vanes of the other electrode, means to direct said electron beams toward the interelectrode spaces of said capacitor, to obtain between said utility terminals a utility capacitance equal to the sum of the capacitance of said capacitor and an electronic capacitance substantially proportional to the product of the intensities of said electron beams, the number of the interelectrode spaces and a factor determined by the size of said interelectrode spaces, and inversely proportional to the accelerating potential applied to said equipotential chamber, and means to simultaneously control the intensity of said electron beams to vary said utility capacitance in accordance with an electric potential applied to said control means.

2. A variable electronic capacitance device comprising an evacuated envelope including means for generating a plurality of parallel laminar electron beams, a low-potential electron accelerating and collecting means constituted of an equipotential chamber having a plurality of elongated slots looking toward said electron beam generating means and including a capacitor having two electrodes connected to a pair of utility terminals and each constituted by a plurality of substantially plane vanes, the vanes of one electrode interleaving with the vanes of the other electrode, means to direct said laminar electron beam toward the interelectrcde spaces of said capacitor to obtain between said utility terminals a utility capacitance equal to the sum or" the capacitance of said capacitor and an electronic capacitance substantially proportional to the product of the total current intensity of the laminar electron beams, the number of the interelectrode spaces and a factor determined by the size of said interelectrode spaces, and inversely proportional to the accelerating potential applied to said equipotential chamber, and means to simultaneously control the intensity of said laminar electron beams to vary said utility capacitance in accordance with an electric potential applied to said control means.

3. A variable electronic capacitance device comprising an evacuated envelope including means for generating a plurality of electron beams, an accelerating and collecting means constituted by an equipotential chamber having a plurality of slots looking toward said electron beam generating means and including a collector electrode portion and a capacitor positioned within said chamber and having two electrodes, each of said electrodes being connected to a utility terminal and formed by a plurality of vanes, the vanes of one electrode inter-Weaving with the vanes of the other electrode, means to direct said electron beams toward the inter-electrode spaces of said capacitor, to obtain between said utility terminals a utility capacitance equal to the sum of the capacitance of said capacitor and an electronic capacitance substantially proportional to the product of the intensities of the said electron beams, the number of the interelectrode spaces and a factor determined by the size of the said inter-electrode spaces, and inversely proportional to the accelerating potential applied to said equipotential chamber, and

means to simultaneously control the intensity of 10 said electron beams to vary said utility capacitance as a function of the electric potential applied to the said control means.

EDOUARD LABIN. ANDRES LEVIALDI. MARC ZIEGLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

